What do you think is the most likely explanation for the Fermi paradox?

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What do you think is the most likely explanation for the Fermi paradox?

On the scale of the universe, the window for an technologically active civilisation is incredibly fleeting. Given that the conditions are also spatially rare this means that the probability of two nearby space civilisations both being in a state to interact, over the distances required, is going to be very low.

And getting worse over time. Possibly young star clusters would be the best place to such interactions to still occur.

On the scale of the universe, the window for an technologically active civilisation is incredibly fleeting. Given that the conditions are also spatially rare this means that the probability of two nearby space civilisations both being in a state to interact, over the distances required, is going to be very low.

And getting worse over time. Possibly young star clusters would be the best place to such interactions to still occur.

Judging by the one example we currently have (ourselves), then more than likely yes.

But both time and the incredible vastness of space itself are doubtless huge factors. Consider this, even if there were 2 Trillion space faring civilizations existing at this exact moment in the Universe, that's still less than 1 per Galaxy and the distance between them (assuming an even distribution) is so vast that the odds of contact (or even detection) is incredibly low.

yes, given that biological species as we know them inevitably go extinct, so will the civilisation they host. The stars around which they are based and their planets also have limited habitability spans. And we have no evidence to the contrary.

yes, given that biological species as we know them inevitably go extinct, so will the civilisation they host. The stars around which they are based and their planets also have limited habitability spans. And we have no evidence to the contrary.

You also have no evidence that ‘habitability’ implies any civilisations beyond Earth’s … yet that doesn’t seem to inhibit the bold claim about ‘the inevitability of species extinction’ elsewhere in the universe?

My own preferred explanation is that the distances are vast and the technology to do such travel very difficult. I'm not generally the "in a million years think of how much more advanced our technology will be" group--I think that we will eventually be able to do nuclear fusion, but even with that it's not an easy trip. Just having the power supply for such a long trip would be difficult.

Or you add that the time span where we radiate signals is also very brief because after a short spell of trying to communicate across space, an advanced civilisation realises that contact might be disastrous and goes quiet. Of course we are not there yet, we are still in metastable formation phase.

sicut vis videre estoWhen we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.Originally Posted by Ken G

My own preferred explanation is that the distances are vast and the technology to do such travel very difficult.

That would make it take a few million years to spread around the galaxy, but that wouldn't explain why it hasn't been done yet by somebody with a multi-hundred-million-year head start on us.

Originally Posted by profloater

Or you add that the time span where we radiate signals is also very brief...

That would explain why we don't observe signals with SETI (especially considering that our own civilization is already not leaking signals out like we were just a few decades ago), but not why we don't seem to be getting lots of physical spacecraft (even small probe-robots) from civilizations with a multi-hundred-million-year head start on us.

* * *

The real problem is that we need an explanation not just for the apparent lack of other present civilizations, but for the apparent lack of them even any time in the last... whatever amount of time has passed since it should have first been possible.

Our planet didn't exist til the universe was about 9 billion years old; couldn't 7 or 8 or 8˝ have been enough?

Even if ours is the oldest of its type because of how long earlier processes must take before this kind of planet could form, life on this planet didn't go multicellular for something like another 3˝-4 billion years; couldn't 1 or 2 or 3 have been enough?

Even if multicellularity really must take that long, once there was a solidly established fauna of multicellular & cephalized animals, it took about another hundred million years to get ecosystems of them permanently living on land; couldn't a few dozen million have been enough?

Once there were plenty of land critters, it would be another couple hundred million years before some of them were warm-blooded; couldn't just 1 hundred million have been enough?

Once we had warm-blooded critters, it would be another couple hundred million years before humans developed; couldn't that last milestone have already been enough just about immediately?

And even at the slow interstellar flight speeds we're dealing with if we stick to reality and not warp drive, we're within a few centuries of being able to build machines that would be able to swarm the galaxy in much less time than each one of those steps took. So even proportionately small adjustments to any one of those periods would have meant somebody should have been able to develop galaxy-swarming technology not just by now, but by long enough ago for their stuff to have been distributed galaxy-wide by now... possibly even outlandish-sounding concepts like before Earth even had its own tetrapods.

That looks like the simplest way to explain the situation is if we're the first or one of the first, which would mean there's a reason why it couldn't have happened sooner somewhere else. So galactic conditions would need to have been more hostile til recently, suppressing the development of technological species & civilizations even in places where it would have otherwise had a head start on us. For example, if the galaxy had a higher rate of gamma-ray bursts at first and the GRBs are only just now beginning to settle down, that would do the trick.

My personal belief is that the reason there appears to be no other technological intelligence out there so far is because we are pretty much alone, at least in our own galaxy.

13.7 billion years seems like a sufficiently long enough time for intelligent life to develop, after all we are proof that it is. But in cosmological terms 13.7 billion years is just a blink of an eye in comparison to the currently considered estimated life span of the universe. We may well be one of a very limited number of first generation intelligent beings to evolve throughout the entire universe, let alone in our own galaxy.

There are too many factors to consider when trying to make reasonable estimates on the odds of intelligent life emerging. We have only life here on Earth as an example and because this is so, we have to make many assumptions based on this. On top of this there appears to be countless "just the right" unlikely circumstances, events & conditions for us to evolve in the first place, that the odds of similar life emerging seems extremely unlikely.

On the other hand what we consider to be intelligent life is only from our perspective. It may well be very abundant throughout our galaxy, but in such a form as we would not easily recognize them/it and they/it may not recognize us either. Don't disclude the fact that we are made up from what we consider to be "normal" matter. Matter that makes up only a very small percentage of we already know exists in the universe. They could be made from dark matter or something else similar that we cannot directly detect and for them vise versa.

On the cusp of yet another trip around the Sun, I found myself wondering how many alien civilizations within this sector of our Milky Way might have already come and gone? That is, bitten the dust due to wholly natural climate change long after their planet had sung its last Auld Lang Syne?

My own preferred explanation is that the distances are vast and the technology to do such travel very difficult. I'm not generally the "in a million years think of how much more advanced our technology will be" group--I think that we will eventually be able to do nuclear fusion, but even with that it's not an easy trip. Just having the power supply for such a long trip would be difficult.

Well said.

Originally Posted by Delvo

That would make it take a few million years to spread around the galaxy,

To calculate how long it would take to spread around the galaxy, you have to consider not only the time it would take to travel from star to star, but also the time it would take between arriving at a new star system and beginning a further trip.

Would it be like driving a car from one city to another, then stopping at a petrol station for just long enough to fill up the tank and buy a hamburger and chips before driving further?

Or would it be more like space flight today, in the sense that they'd touch down in the new system in a much much smaller vehicle than the booster-like device which enabled them to blast off from their home system?

In which case, they couldn't set out on a further interstellar journey before building another interstellar booster. To build another booster, they would first have to do some mining to get the raw materials, then build factories to process the raw materials, etc etc etc...

Plus, while they are doing this, they also have to attend to other things as well, such as finding something to eat on a planet without burger stands...

And even at the slow interstellar flight speeds we're dealing with if we stick to reality and not warp drive, we're within a few centuries of being able to build machines that would be able to swarm the galaxy in much less time than each one of those steps took.

You say we are within a few centuries of being able to build galaxy-swarming machines, but how do you know?

Difficult question for one to answer.
I generally agree with the above comments. Keep also in mind that alien beings that start with different chemistry in the first place, might be quite different from us in many more aspects than we can imagine. Maybe even intelligence comes in different flavors. Also, the aliens might be thinking like 1000 times slower or faster than us. This will make their signals more difficult for us identify as intelligible.

My explanation of the Fermi Paradox is that we are the first technological civilization to emerge in our galaxy, and probably within about a billion light years or so. Yes that is a depressing explanation for it, but it's the only one I know of that explains the universe we see. The biggest reason for this is that we don't see massive numbers of Dyson swarms* around millions or billions of stars, and yes that is a huge problem if there is any technological life anywhere in the galaxy, or even in the universe. Here is why:

Using Humans as a baseline, how long would it take us to turn our solar system into a Dyson Swarm? This will obviously be a guess, but I've seen estimates that say it seems reasonable we could do it in about 100,000 years or so. Maybe it could take a full 1 million years, that's fine. Then assume that we never achieve FTL, and even only traveling at 10% the speed of light we can get to any star in our galaxy in under 1 million years. Also consider that we wouldn't create Dyson swarms 1 star system at a time, but rather would spread outwards in many different directions at once with the colonies we establish each building their own Dyson swarm over the next 1 million years, ect. That's 1 million years to get to the far edge of our galaxy and another 1 million years to build a Dyson Swarm out there, so 2 million years total. This means that we humans can easily fully colonize our own galaxy in under 10 million years without discovering any new physics beyond what we know right now (obviously new advances only make this process easier and quicker). And remember that this means having a full Dyson Swarm around EVERY last star in our galaxy, all accomplished while traveling at slower then light speeds.

Now consider that our galaxy has had the potential to have life bearing worlds for around 10 BILLION years. Now consider that we don't see any evidence, none at all anywhere, of any Dyson Swarms having ever been built anywhere in our galaxy. Or in any nearby galaxies. Or anywhere in our local group. Dyson swarming an entire galaxy is the sort of thing that would be noticeable from across the UNIVERSE, so we would certainly notice if the Andromeda Galaxy has been populated with a technological civilization for the past 3 billion years.

Now, I've seen some comments earlier in this thread saying something to the effect of "well obviously no species last forever", to which I have 3 responses:

1) Once your civilization starts colonizing more then 1 planet your species is essentially immortal. Certainly once it has colonized multiple star systems it's functionally immortal. Sure something can happen to 1 planet that can kill a species off (asteroid impact, killer plague, ect), but I can't think of anything that would cause 2 DIFFERENT planets to both get wiped out at the same time in different star systems. And if you have 1,000 star systems colonized, well there really is no natural event anymore that could threaten you at the species level.

2) You only need 1 civilization to NOT have gone extinct to have massive numbers of Dyson Swarms. Remember, less then 10 million years to fully Dyson Swarm your galaxy, in a universe that is 13 billion years old, so you only need 1 species to do this for it to be noticeable across the observable universe. So you would need to claim that not ONE SINGLE SPECIES has managed to avoid complete self destruction for it to successfully resolve the Fermi Paradox. I am highly skeptical that humans will drive themselves to extinction, it is absolutely NOT a certainty, so I see no reason to assume that 100% of all other intelligent life is doomed to killing themselves.

3) IF (a big if) it is true that no technological species has survived much beyond our current point....well then that is basically what I am saying here, isn't it? After all it doesn't much matter if the lack of technological species is due to none existing or to 100% of them all killing themselves, the end result is that we see a universe in which zero other species has ever gotten to the point that they can build Dyson Swarms.

So, considering all that I think the most likely explanation is that we are the first (and therefore only) intelligent technological species to emerge. Life itself may be common, but technological life appears to be completely missing from our universe (aside from us).

I'd definitely like to hear feedback on what people think of this. Thanks!

*Dyson Swarm- When you disassemble every asteroid and rocky planet in your solar system to turn them into trillions of space habitats to the point that the swarm is absorbing nearly 100% of the energy of it's star. There is enough material in just our asteroid belt plus Mercury to provide several million Earth's worth of living space.

I'd definitely like to hear feedback on what people think of this. Thanks!

OK Dave, here is some feedback for you.

My explanation of the Fermi Paradox is that we are the first technological civilization to emerge in our galaxy, and probably within about a billion light years or so. Yes that is a depressing explanation for it, but it's the only one I know of that explains the universe we see. The biggest reason for this is that we don't see massive numbers of Dyson swarms* around millions or billions of stars, and yes that is a huge problem if there is any technological life anywhere in the galaxy, or even in the universe. Here is why:

Using Humans as a baseline, how long would it take us to turn our solar system into a Dyson Swarm? This will obviously be a guess, but I've seen estimates that say it seems reasonable we could do it in about 100,000 years or so.

Where did you see the estimates? On what information are the estimates based?

Maybe it could take a full 1 million years, that's fine. Then assume that we never achieve FTL, and even only traveling at 10% the speed of light

"only" 10 percent? That's still way faster than any of us humans travel now.

we can get to any star in our galaxy in under 1 million years.

Assuming a space-craft capable of travelling for close to 1 million years without a pit stop...

Also consider that we wouldn't create Dyson swarms 1 star system at a time, but rather would spread outwards in many different directions at once with the colonies we establish each building their own Dyson swarm over the next 1 million years, ect. That's 1 million years to get to the far edge of our galaxy and another 1 million years to build a Dyson Swarm out there, so 2 million years total. This means that we humans can easily fully colonize our own galaxy in under 10 million years without discovering any new physics beyond what we know right now (obviously new advances only make this process easier and quicker).

Why "obviously"? Is it not possible that advances in our knowledge of physics and other sciences will reveal unexpected obstacles against doing some or all of the things you are talking about?

I can think of a couple of things which seemed feasible a few centuries ago, based on what was then known about the laws of nature, but which we know today can't be done. For instance, the alchemists' project of turning lead into gold using apparatus such as cauldrons, retorts, etc...

yes, given that biological species as we know them inevitably go extinct, so will the civilisation they host. The stars around which they are based and their planets also have limited habitability spans. And we have no evidence to the contrary.

I am not so sure this argument works. Most species that have come into existence on Earth have long since gone extinct, but extinct doesn't mean that their lineage died or ended. Many, perhaps most, extinct species evolved into other species rather than simply ending. So, yes, species have a life span, but that doesn't mean the lineage necessarily does. Often it just means it changed enough that we classify it (or them) as a different species, though no doubt closely related.

Where did you see the estimates? On what information are the estimates based?

I've read those estimates several times, but it has been a few years. I did a quick google search and a few quick reads had the estimates from a few thousand years to a few million. Here is one such link that has a bit of good info on Dyson Swarms:

But the point isn't getting the exact amount of time right, it's showing the incredible disparity between the (relatively) short amount of time it would take to build one vs the incredible amount of time the universe has existed for. The time range we are talking about is on the order of thousands to millions of years, but most certainly NOT 10's of billions of years to construct. So even if it takes 100 times longer then I think to build one, that's still only 10 million years to build it and my point is still completely valid.

Though I will say this, if you could come up with a convincing reason as to why it would take 10 billion years to build one, then yes I agree that would invalidate my position. I just think that is an unreasonable amount of time to propose.

"only" 10 percent? That's still way faster than any of us humans travel now.

Of course it is, but so what? Are you claiming that achieving 10% light speed is impossible? Would you also claim that 1% the speed of light is impossible? Because if you allow 1% the speed of light instead of 10%, that's still only 10 million years to the far side of the galaxy in a universe that is 1,000 times older then that. I don't feel that this is any sort of a stumbling block for colonizing the galaxy, why do you think we will never be able to achieve these speeds?

Assuming a space-craft capable of travelling for close to 1 million years without a pit stop...

Actually, I'm assuming a space craft capable of operating indefinitely without a pit stop. The sort of craft I am envisioning would essentially be a small country of hundreds of thousands of people with every industry already present onboard the ship. All the ship would need is an influx of energy to keep going, everything else would be self sustainable even to the point that they could build and replace entire sections of their ship as they went. Though in a practical sense I doubt we would launch a ship directly from Earth to colonize the furthest star in the galaxy, it would probably be a star much closer to it that we had already colonized which would launch that ship.

Why "obviously"? Is it not possible that advances in our knowledge of physics and other sciences will reveal unexpected obstacles against doing some or all of the things you are talking about?

Well, it's possible in the sense that anything is possible, but I don't see it as very likely, no. Building a Dyson Swarm is a matter of industry, we already have the technology. This isn't like trying to build a transporter, or a quantum computer, where we will actively have to discover new technologies to make them work. Just with our present technology and current understanding we already know how to do things like build large space habitats and travel at a % of the speed of light. So no, I don't see what new discovery could be made that would suddenly make building a large space habitat with solar panels a violation of the laws of physics.

I can think of a couple of things which seemed feasible a few centuries ago, based on what was then known about the laws of nature, but which we know today can't be done. For instance, the alchemists' project of turning lead into gold using apparatus such as cauldrons, retorts, etc...

Well, first of all we actually know that it is possible to turn lead into gold, so that was probably just a bad example. But I do get your point here, except that we aren't talking about some NEW technology that we think should be possible one day. Rather the situation is that we can accomplish building a Dyson Swarm using technology we already have. We know that solar panels work. We know that we can build space habitats. We know that we can mine asteroids and refine the materials to turn them into space habitats. Any new technology will either have no effect or make the process easier. We certainly aren't going to discover something new that suddenly makes building large space habitats impossible, but again I will concede that if we do discover something that makes building Dyson Swarms physically impossible then my point is invalid. But is that what you are claiming?

I have to say "space is big". We've barely scratch the surface of our own planet, we constantly find new things in places we never expected. Going to Mars is worse, we seem to have a problem developing viable tools to determine if life is possible. I recall that Phoenix finding ice chunks surprised people, despite the fact that Phoenix was ultimately clobbered* by ice. Not even sure what we are looking for, aside that Barsoonians are right out.

*I know it stopped working from lack of sunlight/power, but being smooched by ice was the kicker.

I think the reason is that it is extremely hard to get abiogenesis. Once you get a protobacterium which can multiply and mutate, natural selection insures evolution and that promotes increasing complexity.
But even a protobacterium would be as complex as iPhone X. To form such without Darwinian evolution may take a trillion years on average, and Earth was freakishly early.

I've read those estimates several times, but it has been a few years. I did a quick google search and a few quick reads had the estimates from a few thousand years to a few million. Here is one such link that has a bit of good info on Dyson Swarms:

But the point isn't getting the exact amount of time right, it's showing the incredible disparity between the (relatively) short amount of time it would take to build one vs the incredible amount of time the universe has existed for. The time range we are talking about is on the order of thousands to millions of years

Thousands to millions? Sounds like there is an incredible disparity between the various estimates you've looked at...

Yes, on the Quora page you linked to, the estimate is millions of years. But back in 1960, Freeman Dyson estimated that "a few thousand years" would be enough. (Quoted in this Popular Mechanics article) Considering the disparity of three orders of magnitude between "thousands" and "millions", can either figure be taken very seriously?

but most certainly NOT 10's of billions of years to construct. So even if it takes 100 times longer then I think to build one, that's still only 10 million years to build it and my point is still completely valid.

Though I will say this, if you could come up with a convincing reason as to why it would take 10 billion years to build one, then yes I agree that would invalidate my position. I just think that is an unreasonable amount of time to propose.

No, I am not going to propose a specific time frame for building a Dyson swarm...

The laws of physics don’t constitute a crystal ball. They don’t enable us to predict what a long-lasting technological civilisation will try to do, nor how long it will take to do it.

Of course it is, but so what? Are you claiming that achieving 10% light speed is impossible? Would you also claim that 1% the speed of light is impossible?

I'm not saying it is impossible for space craft to go that fast. I'm saying that the feasibility of doing so has not been demonstrated. As far as I know, the fastest spacecraft today travel at well under 0.1% of the speed of light.

Because if you allow 1% the speed of light instead of 10%, that's still only 10 million years to the far side of the galaxy in a universe that is 1,000 times older then that. I don't feel that this is any sort of a stumbling block for colonizing the galaxy, why do you think we will never be able to achieve these speeds?
Actually, I'm assuming a space craft capable of operating indefinitely without a pit stop. The sort of craft I am envisioning would essentially be a small country of hundreds of thousands of people with every industry already present onboard the ship. All the ship would need is an influx of energy to keep going, everything else would be self sustainable even to the point that they could build and replace entire sections of their ship as they went.

Sounds great in theory...

Though in a practical sense I doubt we would launch a ship directly from Earth to colonize the furthest star in the galaxy, it would probably be a star much closer to it that we had already colonized which would launch that ship.

I agree that if interstellar colonisation is feasible at all, it would likely be more practical to do it step by step: travel, then colonize, then travel again. But in that case you can't just divide the diameter of the galaxy by the speed of the craft to get the length of time it would take to colonise the lot. You also have to consider how long it would take to establish each of the colonies used as stepping stones.

Well, it's possible in the sense that anything is possible, but I don't see it as very likely, no. Building a Dyson Swarm is a matter of industry, we already have the technology. This isn't like trying to build a transporter, or a quantum computer, where we will actively have to discover new technologies to make them work. Just with our present technology and current understanding we already know how to do things like build large space habitats and travel at a % of the speed of light. So no, I don't see what new discovery could be made that would suddenly make building a large space habitat with solar panels a violation of the laws of physics.

Well, first of all we actually know that it is possible to turn lead into gold, so that was probably just a bad example.

I know it’s possible to turn one metal into another, but not the way alchemists thought they could. Today, the only practical way of producing gold is the old way — prospecting and mining.

But I do get your point here, except that we aren't talking about some NEW technology that we think should be possible one day. Rather the situation is that we can accomplish building a Dyson Swarm using technology we already have. We know that solar panels work. We know that we can build space habitats.

Well, the ISS can be called a space habitat, but it doesn’t recycle everything as your proposed interstellar craft would need to do.

We know that we can mine asteroids and refine the materials to turn them into space habitats.

How many asteroids have we so far mined?

Dyson Swarm proponents talk about taking planets such as Mercury to pieces to provide raw material for their space habitats. You think we have the technology to do that?

Any new technology will either have no effect or make the process easier. We certainly aren't going to discover something new that suddenly makes building large space habitats impossible, but again I will concede that if we do discover something that makes building Dyson Swarms physically impossible then my point is invalid. But is that what you are claiming?

I’m saying that we don’t know whether or not it will ever be a practical proposition — something an actual civilisation is at all likely to do.

Even if a Dyson swarm could theoretically be built, how would its stability compare with the current stability of planetary orbits?

If they’re not stable over a timeframe of billions of years, wouldn’t that explain why we haven’t detected any?

Thousands to millions? Sounds like there is an incredible disparity between the various estimates you've looked at...

Yes, on the Quora page you linked to, the estimate is millions of years. But back in 1960, Freeman Dyson estimated that "a few thousand years" would be enough. (Quoted in this Popular Mechanics article) Considering the disparity of three orders of magnitude between "thousands" and "millions", can either figure be taken very seriously?

Probably not super seriously, no. These are after all rough estimates, and yes I agree with pretty much all of your objections. I just don't agree that your objections make these estimates invalid, and it's because of this: There aren't any estimates that put building a Dyson Swarm at, say 1-10 billion years. If these rough back-of-the-envelope calculations did that, then yes the objections you raised would be completely valid and I probably wouldn't hold the position I currently do regarding the Fermi Paradox. It's simply the huge, HUGE disparity between our best estimates for how long (or short, in this case) it would take to build a Dyson Swarm vs the incredible age of the universe we live in. But like I said before, if I did see a convincing reason for why building a Dyson Swarm would take 10 billion years then I concede that my point is no longer a valid one.

The laws of physics don’t constitute a crystal ball. They don’t enable us to predict what a long-lasting technological civilisation will try to do, nor how long it will take to do it.

Eh, that's actually the entire point of the laws of physics, allowing us to predict what will happen in the future. And I claim that it actually does give us a very good idea of just what a long lasting technological civilization will try to do, because they will be limited by the same laws of physics as us. It would require a fundamental revolution in our understanding of physics to change this significantly. And while it could happen that tomorrow we discover every last physical law of the universe is wrong, I'm not betting on it. I'm basing my opinion of the Fermi Paradox based on what we know NOW. And from what we know now about the laws of physics and how the universe operates, I claim that it shows a barren universe devoid of any technological civilizations.

I'm not saying it is impossible for space craft to go that fast. I'm saying that the feasibility of doing so has not been demonstrated. As far as I know, the fastest spacecraft today travel at well under 0.1% of the speed of light.

Well, I will again say "so what" to that. Why does it matter that humans have not built any super fast space craft yet, when we know that it's entirely possible to go that fast. And you are admitting that you are NOT claiming that such things are impossible, I am going to continue to take for granted that traveling at some % the speed of light is perfectly doable. This is a very odd objection you keep bringing up that you think traveling any faster then we currently can will just be impossible. Sorry, but I flat out reject that. This is a conversation about the future after all, right?

I agree that if interstellar colonisation is feasible at all, it would likely be more practical to do it step by step: travel, then colonize, then travel again. But in that case you can't just divide the diameter of the galaxy by the speed of the craft to get the length of time it would take to colonise the lot. You also have to consider how long it would take to establish each of the colonies used as stepping stones.

For a rough estimate I believe we can, as the stops would probably only be for a few decades, or at most a century or 2 which is insignificant when we are talking about 10 million-ish years. Are you really picturing only a single craft trying to colonize the entire galaxy by itself?

Well, the ISS can be called a space habitat, but it doesn’t recycle everything as your proposed interstellar craft would need to do.

Again, you are trying to make the point of "if we can't do it today, it's impossible". I reject this outright.

How many asteroids have we so far mined?

Show me a law of physics that says "mining asteroids is impossible" and then I will concede we can't do this. Until then, sorry but this is 100% doable on a large industry sized scale.

Dyson Swarm proponents talk about taking planets such as Mercury to pieces to provide raw material for their space habitats. You think we have the technology to do that?

Yes, I know we 100% do because we are currently doing this. After all what would you call digging up pieces of our own Earth to refine into metals that are then shaped into a space habitat and then boosted into orbit? Again, yes we have the technology to do this right now. The only difference between the ISS and a full Dyson Swarm is one of scale.

I’m saying that we don’t know whether or not it will ever be a practical proposition — something an actual civilisation is at all likely to do.

Even if a Dyson swarm could theoretically be built, how would its stability compare with the current stability of planetary orbits?

Considering they would be controlled by humans, very stable. Far more stable then most asteroids I would claim.

If they’re not stable over a timeframe of billions of years, wouldn’t that explain why we haven’t detected any?

You guys are going way over my head on Dyson Spheres. As morbid as this may sound maybe intelligent civilizations figured that it would be more practical just to maintain a low sustainable population rather than build a DS for a trillion inhabitants? Use it's sun for power but not in a way to give itself away?

I think the reason is that it is extremely hard to get abiogenesis. Once you get a protobacterium which can multiply and mutate, natural selection insures evolution and that promotes increasing complexity.
But even a protobacterium would be as complex as iPhone X. To form such without Darwinian evolution may take a trillion years on average, and Earth was freakishly early.

Life as we know it (including bacteria) is certainly very chemically complex. But did this complexity appear due to a freak event, or did it evolve from another, simpler class of multiplying, mutating system?

Here's a paper on this topic published in July last year in the Journal of the Royal Society by Doron Lancet and others.

Life as we know it (including bacteria) is certainly very chemically complex. But did this complexity appear due to a freak event, or did it evolve from another, simpler class of multiplying, mutating system?

Here's a paper on this topic published in July last year in the Journal of the Royal Society by Doron Lancet and others.

I will not be surprised to discover bacteria or other single cells on other planets, apart from the surprise of being able to detect them, but will be very surprised indeed to find large animals and amazed if there is an advanced society. The reason is the declining probabilities and the time taken for those stages on Earth. Plus extinction.

sicut vis videre estoWhen we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.Originally Posted by Ken G

Suppose a race did successfully start to spread throughout their home galaxy at sub light speeds, settling various worlds before moving on. If after a million years of colonization could they even be considered one species any longer, given the difference in adaptation and evolution among the scattered worlds?

I have to say "space is big". We've barely scratch the surface of our own planet, we constantly find new things in places we never expected. Going to Mars is worse, we seem to have a problem developing viable tools to determine if life is possible.

Yes, and perhaps we will learn after a short while that attempting life on Mars will cement the idea that "there's no place like home". It may simply be far better and easier to get our act (and that of aliens) together at home rather than spend much time slugging it out hundreds of trillions of miles from here; "too much squeeze for the juice".

Earth may be a great example of why the Copernican Principle can be hyperbole.

An "intelligent species" will very quickly (we will be there shortly after a meager ~~ 10,000 years or so of "civilization") determine that it can either 1) continue to "grow" its economy, consumption, population, etc and essentially "outgrow" (or trash) its home planet, or 2) opt for a domestic planet "sustainment" model. It would appear that the latter approach would result in the longest duration for such intelligent species on the planet for which its very existence is ideally suited. Yet, under a sustainment model it becomes much more difficult to allocate domestic planet resources to all of the "wasteful" interim steps of space exploration advancement that would be required to even approach the embryonic level of galactic colonization.

Alternatively, under the "growth" model (the one that Earth has been subject to for a few hundred years) it is very likely that a tipping point of resource depletion is reached well before an intelligent species has even made a dent in the wherewithal to become a galactic colonizer.

Generally species are not arranged in a lineage one after the other like beads on a string. A species arises from within another species but that precursor need not be the latest species in a lineage, as sibling species can exist parallel with each other, additionally there is no guarantee of inheritance of all variation of a species within its offspring species, which may come from a particularly small (2 members) and stressed (via a vicariance event) sub-sample of that species. In this way there is also no guarantee of society, technology, intellect, or other forms of complex information being transmitted from parent species to offspring either. The event that separates such species may be a colonisation event without genetic flow back to the source, it may be a cataclysm or extinction event where a significant time gap exists between the end of the parent and the establishment of a successor.

Originally Posted by Darrell

I am not so sure this argument works. Most species that have come into existence on Earth have long since gone extinct, but extinct doesn't mean that their lineage died or ended. Many, perhaps most, extinct species evolved into other species rather than simply ending. So, yes, species have a life span, but that doesn't mean the lineage necessarily does. Often it just means it changed enough that we classify it (or them) as a different species, though no doubt closely related.